Piston pump

ABSTRACT

A piston pump with a piston in a pump chamber has, for controlling an inlet and an outlet of the pump chamber, in a partial region of its peripheral surface, a recess that can be aligned, by a rotational movement about its longitudinal axis, with the inlet or the outlet. By means of a stroke cam gear, the piston can be caused to carry out a lifting motion within the pump chamber. The stroke cam gear is formed by a peripheral guiding path of an adjusting element, which can be swiveled about a stationary axis of rotation, and a radial projection at the piston, which engages this guiding path.

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] This invention relates to piston pumps and, more particularly, this invention relates to piston pumps of the type with a piston in a pump chamber which, for controlling an inlet and an outlet of the pump chamber, has, in a partial region of its peripheral surface, a recess that can be aligned, by a rotational movement about its longitudinal axis, with the inlet or the outlet and which can be caused to carry at a lifting motion within the pump chamber by a stroke cam gear.

[0002] This application claims the priority of German application No. 100 56 630.8, filed Nov. 15, 2000, the disclosure of which is expressly incorporated by reference herein.

[0003] A piston pump of the above type is the object of DE 43 37 326 A1. This piston pump is constructed very simply, because the opening and closing of the inlet and the outlet of the piston pump take place through a rotational movement of its piston and, at the same time, a lifting motion is derived from this rotational motion of the piston, in that a flange, which is aligned obliquely, is disposed, on its peripheral surface and is embraced in pliers fashion at one side of the piston, so that a stroke cam gear results. An electric motor drives the piston pump and sets the piston in the required rotational movement directly or over a transmission.

[0004] The known piston pump is intended for water piks. For these it is important that water sprays out of the nozzle of the water pik at a high pressure and with a pulse frequency, which is optimum for massaging the gum and for cleaning the teeth. However, since the gums of different persons have different sensitivities, it is desirable that the pressure and the amount of water, spraying out of the nozzle, can be controlled. For this purpose, a d.c. motor could be provided to drive the piston pump and to adjust the rpm of the pump electrically. However, it is a disadvantage that, as the rpm is reduced to decrease the amount conveyed as well as the pressure, the number of piston lifts per unit time and, with that, the pulse frequency of the emerging water would also be changed. However, by varying the pulse frequency, one deviates necessarily from the pulse frequency, which is optimum for cleaning and massaging the gum.

[0005] Aside from these functional disadvantages resulting from adjusting the rpm of the electric motor, there is the economic disadvantage that, in order to make it possible to adjust the rpm, the electric motor would have to be constructed as a d.c. motor. Moreover, driving such a piston pump with a d.c. motor is significantly more expensive than driving it with an a.c. motor, particularly since a rectifier and transformer are required for a d.c. motor.

[0006] It is, therefore, an object of the present invention to construct a pump of the type named above so that the conveying performance and, with that, the pressure can be adjusted without changing the rpm of the driving mechanism of the piston pump and, with that, without changing the lifting frequency of its piston.

[0007] Pursuant to the invention, this object is accomplished by forming the stroke cam gear by a peripheral guiding path of an adjusting element, which can be swiveled about a stationary axis of rotation, and by a radial projection at the piston, which engages this guiding path.

[0008] Because the adjusting element with the guide path can be swiveled pursuant to the invention, it becomes possible to increase the lift of the piston by increasing the inclination of the adjusting element relative to the piston. As a result, it becomes possible to change the conveying output of the piston pump and its conveying pressure without having to change the lifting frequency. If the inventive piston pump is used for a water pik, the piston of the piston pump can be driven constantly with such an rpm, that the resulting pulse frequency is constant and optimum for the action of the water pik, even if the output is changed.

[0009] The construction of the piston pump is particularly simple if, in accordance with an advantageous development of the invention, the projection is formed at the free end of the piston by a pin with a sliding block, the pin protruding radially from the piston, and the sliding block engaging the guiding path of the adjusting element.

[0010] The adjusting element can be constructed very simply and disposed pivotably, in that it is constructed as a plate, which overlaps the piston with a borehole having the guiding path and, for forming the axis of rotation, has two pegs, which are aligned at opposite sides with the guiding path and engage pivotably a base of the piston pump, attached to the housing.

[0011] If, in accordance with a further development of the invention, the axis of rotation tangentially through a guiding path in the region of the point of application of the sliding block of the radial pin, it is achieved that the top dead center of the piston does not change in the cylinder of the piston pump. As a result, the dead volume of the piston pump always remains constant and a small value can be selected for it.

[0012] It is particularly advantageous if the adjusting element is constructed to swivel from a position, extending at right angles to the longitudinal axis of the piston into a tilted position, extending obliquely to the longitudinal axis of the piston. By these means, it becomes possible to vary the output of the pump infinitely from a value of zero up to a maximum output, fixed by the maximum inclined position of the adjusting element.

[0013] Friction between the sliding block and the guiding path is particularly low if the sliding block is constructed as a roll body, which is supported rotatably on the pin.

[0014] Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a plan view of a piston pump of the present invention;

[0016]FIG. 2 is a longitudinal section through the piston pump taken along the line II-II pf FIG. 1;

[0017]FIG. 3 is a perspective representation of a piston of the piston pump; and

[0018]FIG. 4 is an exploded representation of the most essential parts of the inventive piston pump.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019]FIG. 1 shows a pump base 1 on which an electric motor 2 is held. The motor 2, which is rotating at a constant rpm, drives a piston 4 through a transmission 3. The piston 4 leads into a pump housing 5, which has a pump chamber 6 with an inlet 7 and an outlet 8.

[0020] The output of the piston pump at a constant stroke frequency can be adjusted by an adjusting element 9, which is disposed so that it can swivel about an axis of rotation 20.

[0021] On the pump base 1, the sectional representation of FIG. 2 shows the pump housing 5, into which the piston 4 protrudes and which the pump chamber 6 adjoins. Outside of the pump chamber 5, a radial pin 10, which is provided with a sliding block at its free end, protrudes out of the piston 4. This sliding block 11 engages a peripheral guiding path 12 of the adjusting element 9. If the adjusting element 9 is tilted from a position at right angles to the longitudinal axis of the piston 4, as shown in FIG. 1, then the piston 4, which is rotated by the electric motor 2, carries out a back and forth stroke motion in the pump housing 5. For this purpose, the piston must be connected non-rotationally yet axially displaceably by means of a connecting part 13 with the transmission of the electric motor 2. Together with the guiding path 12 and the pin 10, the adjusting element 9 forms a stroke cam gear 14.

[0022] The sliding block 11 can be constructed as a spherical head, as shown in FIG. 2. It is however also possible to dispose a ball bearing as sliding block on the pin 10, so that there is rolling friction instead of sliding friction in the guiding path 12.

[0023]FIG. 3 is highly enlarged in comparison to FIG. 2 and shows, in perspective, the piston 4 with its radial pin 10, which has the sliding block 11 at its free end. Moreover, a recess 15 can be recognized in the front region of its shell. This recess 15 extends over a partial region of its peripheral surface, so that, depending on the angular position of the piston 4, the inlet 7, or the outlet 8 shown in FIG. 1, is connected with the pump chamber 6.

[0024] The exploded diagram of FIG. 4, above the pump base 1, shows the piston 4 and a motor seat 16 for the electric motor 2 shown in FIGS. 1 and 2. Still further above, the adjusting element 9 is shown. This is constructed as a plate and has a borehole 17, through which the piston 4 engages with clearance. In the inner shell of the borehole 17, the guiding path 12 is shown, which has already been shown in FIG. 2 and which is engaged by the sliding block 11. To form the axis of rotation 20, the adjusting element 9 has two pegs 18, 19 at opposite sides. The two pegs 18, 19 are aligned with one another and lie on the axis of rotation 20, which passes tangentially through the guiding path 12, where the sliding block 11 carries out its rotational movement. 

What is claimed is:
 1. A piston pump comprising a piston in a pump chamber having an inlet and an outlet, said piston having, in a partial region of its peripheral surface, a recess that can be aligned by a rotational movement about its longitudinal axis with the inlet or outlet to thereby control the inlet and the outlet of the pump chamber, said piston pump further comprising a stroke cam gear to cause the piston to carry out a stroke motion within the pump chamber, wherein the stroke cam gear comprises an adjusting element which can be swiveled about a stationary axis of rotation and which comprises a peripheral guiding path and a radial projection at the piston which engages the guiding path.
 2. The piston pump of claim 1, wherein the projection comprises a pin with a sliding block protruding radially from the free end of the piston and the sliding block engages the guiding path of the adjusting element.
 3. The piston pump of claim 2, wherein the adjusting element is constructed as a plate which overlaps the piston with a borehole having the guiding path and, for forming the axis of rotation, has two pegs which are aligned at opposite sides with the guiding path and engage pivotably a base of the piston pump attached to the housing.
 4. The piston pump of claim 3, wherein the axis of rotation passes tangentially through the guiding path in the region of the point of application of the sliding block of the radial pin.
 5. The piston pump of claim 1, wherein the adjusting element is constructed as a plate, which overlaps the piston with a borehole having the guiding path and, for forming the axis of rotation, has two pegs, which are aligned at opposite sides with the guiding path and engage pivotably a base of the piston pump, attached to the housing.
 6. The piston pump of any one of claims 1-5, wherein the adjusting element is constructed for swiveling out of a position, extending at right angles to the longitudinal axis of the piston into a tilted position, extending obliquely to the longitudinal axis of the piston.
 7. The piston pump of any one of claims 1-5, wherein the sliding block is constructed as a roll body, which is mounted rotatably on the pin. 